I just finished reading an interesting bit of Scottish and tartan history. It seems that before the Elizabethan Period, kilts and fly plaids were mixed with no particular attempt at matching (great kilts excepted, of course). Early portraits reportedly show Highlanders wearing whatever colors came to hand. In the Battle of Culloden, units were recognized by the bit of plant material (Bog Laurel for one) stuck in their bonnets, not by the plaid they wore.

Based on this (and they may be wrong), there is no really "proper" highland kilt attire, except the basics of formal, or semi-formal convention. Prince Charles wears black shoes with a brown sporran and belt, so is it really "proper" that everything match, or be of complementary colors?

Having said that, I agree that matching and complementary colors present the best appearance overall, but if one is comfortable with what he has on, shouldn't that be the primary criteria?

The following website was what I read.

http://www.scottish-wedding-dreams.com/tartans.htm